"I see nothing wrong with law abiding citizens owning a gun though."

Robert Steinhauser was a law-abiding citizen, until he took his legally owned guns into school and shot all those people.

From the accounts I've read it seems he was living out some weird fantasy, dressed up in costume as some kind of Ninja. The problem being that the lethal toys he needed to turn the fantasy into reality were there at hand for him in a country where there are said to be around 20 million guns in private hands.

What all this reminds me of is Lyndsey Anderson's film "If".